Some Devices no longer updating.

[POBMIS]

Currently running 4.2.0.60.
After a past upgrade in November, 17 "devices" are no longer updating and show a date of 11/22/11. They do reply to a ping however.
The devices in question are of the same manufacturer and type.
All other devices on network are updating.
My first assumption is that these devices to no update, but they did when first added to network (at least for a few months).
Thank you for any ideas and tips.

[Hemoco]

Please contact us at support@lansweeper.com and provide us with screenshots of the following:
- Your web console landing page.
- Webpages of one or two affected devices.
- Your IP Range Scanning settings. The IP Range Scanning tab can be found in the configuration console under Scanning Servers\Your Server. Please show us your "IP ranges" and "IP exclusions".